M. J.Styzen, L R. Reugger. Polymer mud problems, p. 19-20.

Journal ofNannoplankton Research, 16, I, 1994.

POLYMER MUD: PROBLEMS AND SOLUTION
Michael J Styzen, Shell O.ffshore Inc. P.O.Box 61933 New Orleans, LA 70161, USA
Laura/ee R. Reugger, Consultant, 102 Big Pine Dr. Covington, LA 70433 USA

During 1986 and early 1987, we noticed a marked reduction in the abundance of nannofossils present in samples
from offshore Gulf of Mexico exploratory wells. Thisproblem was of great concern to us and, for a time, brought
into question whether nannofossil biostratigraphy would
be as useful in deep water settings as we had earlier hoped.
Strata deposited at low depositional rates in a bathyalenvironment, above CCD, should contain abundantnannofossil floras. Their near absence in samples fromwells drilled into such sediments was a mystery.
In the summer of 1987, during the drilling of thefirst wells at Prospect Auger (Garden Banks block 470 and471}, the technician who prepared our slides reported
increasing problems with sample processing. The standard procedure at that time was: A small cut (approximately2 cc) of unwashed cuttings was placed in a vial, water
added and mixed using a vortex mixer. A drop of theresulting suspension was placed on a microscope slideusing a capillary tube. Finally the slide was dried on a hot
plate and a cover glass was affixed.
Samples from the wells in question would bead up
on the slide and not spread evenly. The technician sent us
a representative batch of the problem samples. They
exhibited some very unusual properties. When the samples were mixed with water in the vial, the resulting
suspension had a thick plastic-like consistency viscousenough to stand up a capillary tube. If the samples weremixed with more water in a larger container, a similar
consistency resulted without apparent loss of viscosity.
Once water was added, any attempt to remove it byphysical means was unsuccessful. Several samples were
centrifuged for ten minutes at 3500 r.p.m. without any
material coming out of suspension. When the samples inthe vials were oven-dried the sediment retained very muchthe same volume as when wet, and was overgrown by anarray of fibrous crystals.
The unusual characteristics of the samples wereintriguing and suggested a cause for the paucity of ourobserved floras. The ability of the samples to occupy any
reasonable volume showed us that our specimens weremore widely distributed in a larger volume of mud thanpreviously. The assemblages were being diluted. We
concluded that the unusual properties observed were nota natural phenomenon and some sort of polymer drilling
mud was responsible. The problems proved to be due tosalt polymer mud, which was first used successfully byShell Offshore Inc. in June 1986 (Cheatham et al., 1987).
This type of polymer solved a plethora ofdrilling problems
but wreaked havoc on attempts at nannofossil
biostratigraphy.
We initially tried rinsing the drilling mud off thecuttings. This proved unsuccessful as the polymer was
tenacious and even a small amount produced the problems
described above. The vigourous washing necessary toremove all the drilling fluids from the ·samples also
removed most of the nannofossil bearing shale. Later

experimentation also showed that the polymer reactedwith any expandable formation clays along with thedrilling mud. It was clear that the polymer had to beremoved or neutralized, without removing the clay fraction. We consulted our drilling department and several
drilling mud companies and received numerous suggestions; none worked. Research efforts in those circles
generally are aimed at increasing and preserving the very
properties we found undesirable. In late 1987, one mudcompany kindly provided us with samples of all theirpolymer products. Over a period of three months weexperimented with the polymer samples and samples fromthe affected wells. Two chemicals proved to be effective indisassociating the polymer from the clay particles: sodium
hypochlorite (chlorine bleach) and methanol. Both areequally effective, but methanol is flammable and more
toxic so we elected to employ bleach. The entire proceduremust be followed for successful results. Simply adding a
few drops of bleach to your nannofossil preparation likely
does more harm that good (see note in step 2 below).

Procedure
1. Place approximately 1 ml unwashed cuttings in a 15 m1
centrifuge vial.

2. Add full strength bleach (or methanol) to the 12 mlmark.
Note:Do not add water! Do not use dilute bleach!
Gaffey and Bronnimann ( 1993) report that dilute bleachetches carbonates while full strength it has no effect.
3. Spin stir on a vortex mixer to thoroughly mix sample.
4. Place in a centrifuge and run at high speed (3500 rpm}
for 30 seconds.
5. Decant liquid and retain residue in the centrifuge tube.
Note:Steps 1-5 serve to break the bonds of thepolymer to the mud. The polymer is still present. Ifthesamples were used at this point the polymer-related
problems would still occur.
6. Add water to the 12 ml mark; stir on a vortex mixer.
7. Centrifuge on high speed for 30 seconds.
8. Decant liquid; retain residue in the centrifuge tube.
Note:The decanted liquid at this point is a gel-like
substance that is either translucent or dark brown
depending on whether lignosulfate is present in themud system.
9. Repeat steps 6-8 until decantant is all water or desired
viscosity is reached (usually two or three rinses).
Note: We have found that a very small amount ofpolymer left in the sample enhances spreadability
without significantly diluting the flora.
lO.Make nannofossil slides in the normal way, from theresidue.

Remarks
The use of various polymers in drilling fluids has becomecommon place in oil and gas drilling operations since themid eighties. Since that time, treating nannofossil samples for polymers has become part of our standard procedure. The effects of this procedure on our sample quality========================== 19 ==========================

JoumalofNannoplanktonResearch, 16, I, 1994.

is phenomenal. The number of fossils observed on a slide
after the polymer has been removed has been found to beup to eight time greater than in the same sample beforetreatment. This procedure has had a profound effect on thequality of our interpretations. It is presented here in thehope that the technique will improve results of all workers
who work with ditch cuttings from polymer mud systems.

M. J.Styzen. L. R. Reugger. Polymer mud problems, p. 19-20.
REFERENCES
Cheatham C.A., Dupal K., Eaton L.F. & Gonzalez R. 1987:Salt-polymer drilling mud for Gulf of Mexico: Semiannual Technology Highlights- First Half 1987; Shell Oil
Company and Subsidiaries Production Department Houston, Texas. (Shell internal publication).
Gatfey S.J. & Bronnimann C.E. 1993: Effects of bleaching onorganic and mineral phases in biogenic carbonates.
J. Sed. Petro/.,.63, 752.

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